Supertex’s PS30 constant-frequency (67 kHz), constant duty-cycle LED driver provides high power factor correction (PFC) for dimmable off-line LED bulb and tube applications. The device is intended to drive a single-switch, single-inductor power converter (flyback for isolated versions and buck-boost for non-isolated versions) directly from a 110- or 220- V ac line for power levels up to 20 W. It provides smooth dimming to extinction for dimmer types such as leading-edge and trailing-edge dimmers, and dimmers with microprocessor controls. The PFC LED driver operates from a 10-V shunt regulator derived from the power-supply snubber, eliminating feedback components and the optocoupler. Line-induced brightness variation is minimized, and openvoltage protection prevents open-circuit failure. The PS30 is designed to implement a simpler, lower-cost open-loop solution—proprietary control techniques mitigate output-current amplitude variation typically experienced with open-loop design. Also, proprietary dimming circuits help ensure proper operation with different triac dimmers. A PS30DB1 demo board, which provides a 6.3-W design solution, achieves 93% PFC and over 81% efficiency with ±4% current accuracy.
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